1. Field of the Invention
The present invention relates to radiation curable compositions useful in visible light image projection systems. More specifically, the present invention relates to (meth)acrylate-based compositions that contains two or more free radical photoinitiators in both the visible and UV light ranges.
2. Brief Description of the Art
Visible light image projection systems are a recent development in the three-dimensional solid imaging field. Such systems are an alternative to stereolithographic solid imaging systems using laser scanning. Image projection systems use visible light to initiate photocuring and are an extremely low cost approach to solid imaging when compared to stereolithographic systems that use laser beams to initiate photocuring. The image projection process may employ an endless flexible light permeable belt coated with a resin which is moved through an exposure station where a digital light projector imagewise exposes the resin through the light permeable belt to imagewise solidify and form a cured resin layer. The light source is above the belt and a build platform which supports the solidified resin layer below the endless belt. After this imagewise exposure and curing, the imaged and cured resin layer is separated from the belt and remains adhered to the build platform on top of previously exposed layers. This process is then repeated until a desired three-dimensional object is made. Resin layers are repeatedly coated onto the endless belt and then imagewise exposed. Each solid resin layer is then separated from the belt and remains adhered to the support platform with subsequent exposed layers until the completed object is formed.
The curable resins used in image projection systems need to have a combination of desirable properties. Preferably, such resins should have little or no surface tackiness and should have reduced adhesion properties so they can be easily removed from the endless belt, yet have sufficient physical properties so that they form useful three-dimensional objects. Moreover, it is desirable they produce a dry part that the end user can handle right off of the image projection machine without any danger of sensitization resulting from skin contact with the formed three-dimensional object.
There is a need today for better-performing resin compositions that will work with these image projection systems. The present invention offers a solution to that need.